Scaling and ecomorphology of lagomorph body shape and appendicular skeleton

Body shape is one of the most prominent features of phenotypic variation. Yet, mammalian body shapes are poorly quantified and the underlying components contributing to its diversity and its relationship to other skeletal components are rarely tested. Here, we use lagomorphs (hares, rabbits, and pikas) to (1) investigate which components of the skeleton contributed the most to body shape diversity defined using the head-body elongation ratio (hbER), (2) examine the relationships between body shape and limb lengths, and (3) test how body size, morphotype, burrowing behavior, and locomotor mode influenced variation in body shape and appendicular morphology. We quantified body shape and functional proxies of the limbs in 40 species. We found relative rib length and elongation or shortening of the thoracolumbar region contributed the most to body shape evolution across lagomorphs. Second, we found that only hares and rabbits exhibited a significant relationship between limb length and body shape, where more elongate species exhibit relatively shorter limbs. Lastly, we found that models incorporating body size, estimated using the geometric mean of all skeletal traits, were the best predictors of body shape and most appendicular traits, whereas models incorporating burrowing behavior or locomotor mode were poor fits. These results indicate that larger lagomorphs tend to exhibit more stout bodies with longer, more gracile forelimbs, whereas smaller lagomorphs tend to exhibit more elongate bodies with shorter, more robust forelimbs. Overall, this work contributes to the growing understanding of body shape evolution and demonstrates the importance of not omitting size in ecomorphological analyses.